WO2013136150A1

WO2013136150A1 - Method for dual-energy mammography

Info

Publication number: WO2013136150A1
Application number: PCT/IB2013/000344
Authority: WO
Original assignee: Space Research Institute (Iki); Russian Scientific Center Of Roentgeneoradiology
Priority date: 2012-03-11
Filing date: 2013-03-11
Publication date: 2013-09-19
Also published as: RU2495623C1; RU2012108684A; EP2638857A1; US20150030122A1; DE112013001364A5; JP2015509417A

Abstract

The invention relates to a method for a dual-energy mammography. The aim of the invention is to be able to detect earlier microcalcifications as precursors of an oncologic tumor in the mammary gland. According to the invention, this is achieved in that a reference pattern with known density, thickness, and effective atomic number distributions is arranged adjacently to the mammary gland. The parameters of the relationship between the atomic number and the difference or the ratio of the logarithms of the number of photons which pass through the mammary gland at two different radiation energies without interaction are determined using the reference pattern. The distribution of the atomic numbers in the mammary gland is presented visually using said relationship.

Description

Method for two-energy mammography

The invention relates to a method for two-energy mammography according to the preamble of claim 1.

The invention can be used in medicine, namely in methods for the diagnosis of benign and malignant diseases of the mammary gland.

The precursors of an oncological tumor in the mammary gland are microcalcifications. These have a considerably larger effective atomic number (Z = 12-14) over the effective atomic number of a healthy tissue (Z = 6.5-7.5). The presence of microcalcifications is basically sufficient Prerequisite for the formation of an oncological tumor. Microcalcifications, whose size is less than 200 pm, are particularly dangerous because they are currently not recognized in a radiographic mammography. A cancerous tumor also has an increased effective atomic number. This is related to a different distribution of carbon and oxygen (Antoniassi M., Conceicao ALC Study of effective atomic number of breast tissues deter- mined using the elastic to inelastic scattering ratio // Nuclear Instruments and Methods in Physics Research Section A: Accelerators , Spectrometers, Detectors and Associated Equipment, 2011.V.652, No. 1, pp. 739-743.).

The method according to the invention for two-energy mammography makes it possible to detect microcalcifications more reliably than hitherto and in earlier stages of the disease than hitherto and to render an oncological new formation sharper than hitherto possible with conventional diagnostic methods.

The most meaningful diagnostic procedure for early non-palpable cancers is X-ray screening mammography. This method is based on the effect that the degree of x-ray absorption in the different tissues is different. It is therefore the visualization of the quantity distribution of the photons that have passed through the mammary gland without any interaction:

in which

- the initial photon number

the mass coefficient distribution of the total absorption coefficient over the beam line (the mass absorption coefficient is dependent on the energy of the output photon and on the effective atom number of the mammary gland section), p (x) density distribution along the radiation vector and

d - mammary gland thickness along the radiation vector.

The mass absorption coefficient is proportional to the effective atomic number (within its narrow range of variation).

Thus, the conventional X-ray mammogram is the representation of the non-linear distribution of the product of thickness, density and the effective atomic number in the mammary gland. Fig. 1a shows an example of a conventional mammographic mammogram with microcalcifications.

The density distribution in the mammary gland (ducts, vessels, benign formations, etc.) often covers the small microcalcifications that may be present on the mammogram. Despite the collimators used, the detectors still detect the scattered X-ray radiation. Because of this, the mammary gland on the mammograms is not depicted with enough detail. This, in turn, makes detection of small micro-calcifications even more difficult. Only over 200 μητι large micro-calcifications can be identified with certainty. Smaller microcalcifications can only be detected on homogenous artificial samples (phantoms).

In order to increase the sensitivity of mammograms to the distribution of the effective atomic number, the method of two-energy difference Mammography (two-energy subtraction mammography) applied. It is protected by numerous patents (Dual energy rapid switching imaging system, U.S. Patent 4,541,106, 1985; Dual-energy system for quantitative radiographic imaging, U.S. Patent 5,150,394, 1992; Dual energy x-ray imaging system and method for radiography and mammography, US Pat. No. 6,683,934, 2004).

The method for two-energy difference mammography is described in detail in the following: Lewin, JM, Isaacs, PK, Vance, V., Larke, FJ: Dual-energy contrast-enhanced digital subtraction mammography: Feasibility, Radiology, Volume 229, Number 1, 261-268, 2003.

According to this method, two mammograms are generated with two different energies of the output radiation. Thereafter, their logarithmization and subtraction (difference formation) takes place:

in which

L, H indices corresponding to the lower and upper energy values, and

Linearization coefficients are.

Thus, two-energy difference mammography is the visualization of the linear distribution of the product of the effective atomic number and density.

Fig. B shows an example of a differential mammogram for the same mammary gland. The two-energy difference mammogram is considerably sharper, because the scattered radiation is suppressed. However, the representation of individual sites in the mammary gland is dependent on both the effective atomic number and its density and thickness. This also impedes the detection of tiny microcalcifications (only larger microcalcifications are visible).

In order to reduce the degree of influence of the density and thickness variations on the mammogram, a method of two-energy division mammography (method for differential diagnosis of mammary gland, Patent RU 2391909, 2008) has been proposed.

This method of two-energy division mammography is described in particular detail in the following references: 1. V.A. Gorshkov, N.I. Rozhkova, SP. Prokopenko. Two-energy Division Mammography. Method for nonlinear analysis for cardiology and oncology. Physical approaches and clinical practice. Issue 2. OOO KDU Verlag, 2010. p. 173-191. 2. V. Gorshkov, N. Rozhkova, S. Prokopenko. Dual-energy-dividing-mammography, International Workshop on Digital Mammography, 2010. Girona, Spain. PP.606-613.

In two-energy division mammography, the ratio of the above-mentioned logarithms is visualized:

From this it can be seen that this ratio is independent of the density. It is determined only by the distribution of the effective atomic numbers.

Fig. 1c shows an example of a division mammogram of the same mammary gland.

The density and thickness variations are less pronounced on the division mammogram than on the differential mammogram. The nipple of the thoracic gland is virtually invisible on the differential mammogram (it has a very small thickness and is therefore also shown on the division mammogram with practically the same density as the mammary gland).

However, the mammogram shown in Figure 1c shows vessels and ducts and other density variations. This is due to the fact that equation (3) only applies to a radiation spectrum with uniform energy. For real X-ray tube spectra, which include both characteristic and bremsstrahlung, it is impossible to suppress the density and thickness variations in the mammograms.

An effective diagnosis of breast gland disease requires visualization of effective atomic number, density, and their convex combina- tion. It is an object of the invention to develop a method for two-energy mammography, which allows detection of smaller Mikrokalzifikationen than before. The stated object is solved by the features of claim 1.

To the mammograms with the following represented distributions: an effective atomic number that is invariant to the density variation, - a density of the effective atomic number that is invariant to the variation,

the convex combination of the effective atomic number and density,

To get a method according to the invention for two-energy difference and division mammography is proposed.

The invention will be explained in more detail with reference to the drawings. Show it:

Fig. 1 Examples of mammograms

1a - X-ray screening mammography,

FIG. 1b - Two-energy difference X-ray mammography, FIG.

Fig. 1c - the same for a division mammogram,

Fig. 1d - the same for a division difference mammography with the distribution of the effective atomic number Fig. 2 shows a section of a conventional mammogram (Fig, 2a) and a division-difference mammogram (distribution of the effective atomic number) (Fig. 2b) , Fig 3 sections of the mammograms:

Fig. 3a - in the X-ray screening mammography;

Fig. 3b - in the two-energy difference X-ray mammography; Fig. 3c - the same for division mammography;

Fig. 4d - the same for the division difference mammography in a distribution of the convex combination of the effective atomic number and density and

4 shows a diagram of the method for determining the distribution of the effective atomic number, the density and their convex combination.

It follows:

In the continuous spectra, the numerical values of both the differences and the ratios of the above-mentioned logarithms are linearly related to both the density (at constant thickness) and the effective atomic number (within their narrow range of change). Consequently, the visualization of the distribution of the effective atomic number and the density is possible on the basis of the following equations:

The distribution of the convex combination of their unit sizes is defined as

where k is the coefficient

is. Standardization of the effective atomic number:

Normalization of the effective density:

The problem is determining the coefficients

In order to estimate these coefficients, in addition to mammography, a comparative pattern with known distributions of density, thickness, and effective atomic number is used (their characteristics are similar to that of the mammary gland). These coefficients are determined from the mammograms of the comparative pattern with two energies. The publication WO 99/45371 describes a method in computed tomography in which a comparison pattern is positioned next to a body part to be examined. This effect as well as the numerical restoration of the distribution of the effective atomic number and the density are the characterizing features of the method according to the invention.

In this description are

Matrices defining the values of the corresponding characteristics as i, j-ge pixels of a detector (the mammogram).

The coefficients

are scalar sizes. FIG. 1 d shows an example of a distribution of the effective atomic number which was calculated with the help of the two-energy-division-difference mammography according to the invention on the basis of two mammograms. These two mammograms were generated at two different plate voltages of the x-ray tube. As a comparison pattern, a graphitic prism (simulating tissue of the mammary gland) with aluminum strips of different thickness (simulating microcalcifications) was used.

On the division difference mammogram, virtually no vessels and courses are more visible. The healthy parts of the mammary gland are displayed with the same light density.

FIG. 2 shows sections of a conventional (FIG. 2a) and a two-energy-division-difference mammogram (FIG. 2b) (effective atomic number distribution and density distribution). Large micro-calcifications can be made on the con- recognize an adequate mammogram well enough. However, the small microcalcifications that are clearly visible on the division-difference mammogram are not visible. Some aggregations of small microcalcifications from the division-difference mammogram on the conventional mammogram look like a large granule.

Both a cancerous tumor and the microcalcifications have an increased density in addition to the increased effective atomic number. Therefore, such inclusions can be better identified by means of a convex combination of their unit sizes (normal values).

FIG. 3 depicts the effectiveness of visualizing the convex combination of the identified unit sizes of effective atomic number and density. From this it can be seen that the tiniest microcalcifications (which are not recognizable in conventional screening mammography and difficult to detect in the differential mammogram) can be identified effectively enough here in the distribution of the convex combination of the unit quantities of effective atomic number and density ,

Thus, CDMA allows mammary diseases due to the formation of microcalcifications to be recognized at an earlier stage in their development.

The invention is carried out in the following steps: 1. The comparison sample with the known density, thickness and effective atom number distributions is placed next to the mammary gland on the table top of the mammograph.

2. Two mammograms are recorded at low and high anode voltage. 3. The coefficients from formula 4 are calculated using the comparison pattern.

4. The distribution of the effective atomic numbers, the density and their convex combination in the mammary gland is visualized by means of the calculated coefficients.

4 shows the functional principle for carrying out the method for two-energy divisional difference mammography.

1. The reference sample with the known density, thickness, and effective atomic number distributions is placed next to the mammary gland on the table top of the mammograms.

2. Two mammograms are recorded at low and high anode voltage. With their help, the distributions of the ratios of the output photon quantity No to the photon quantity detected by the detector are determined for both the reference pattern and the mammary gland at low (L) and high (H) energies.

3. On the basis of the determined distributions, the logarithmic distributions of the ratios and the differences for the reference sample and for the mammary gland are determined:

4. Due to the distributions of the logarithmic ratios and differences for the comparison pattern, the coefficients become

of the relation of the effective atomic number and the density with the ratio and with these logarithms calculated in the following equations:

5. On the basis of the determined coefficients, the distributions of the ratios (β) and the difference (α) of the logarithms are converted into the distributions of the effective atomic number and the density:

These relationships are visualized for diagnosis. 6. Carrying out the standardization of the effective atomic number and the standardization of the effective density:

7. Using the distributions of the effective atomic number and the density, their convex combination is calculated and visualized:

attachment

Bibliographic information

1. Antoniassi M., Conceicao A.L.C. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment. 2011. V. 652, N ° 1 P. 739-743.

2. Frank Carroll, M.D. et al., Tomography Imaging Using Monochromatic X-rays and Mosaic Crystals in the Geometry of Stationary Source, Object and Detec- tor.

Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232-2675.

3. Johns, Paul C. et al., Dual Energy Mammography: Initial Experimental Results, Medical Physics, May / Jun. 1985, pp. 297-304 4. Lewin, JM, Isaacs, PK, Vance, V., Larke, FJ: Dual-energy contrast-enhanced digital subtraction mammography: feasibility. Radiology, Volume 229, Number 1, 261-268, (2003). 5. Lewin JM et al. Clinical comparison of full-field digital mammography and screen-film mammography for breast cancer detection, AJR Am J Roentgenol., 2002 Sep; 179 (3): 671-7. 6. Weij., Hadjiiski LM et al. Computer-aided detection systems for breast masses: comparison of performances on full-field digital mammograms and digitized screen-movie mammograms, Acad. Radiol., 2007 Jun; 14 (6): 659-69. 7. A method for the diagnosis of breast cancer for determining the distribution of the effective atomic number, Patent RU 2391909, 2008 9. US 6 173 034 B1 10th US 2009/0304253 A1 1 1. WO 01/040754 A3

Claims

claims

1. A method for two-energy mammography with the generation of a mammogram with two different radiant energies,

characterized,

that, in addition to the mammary gland, a reference pattern with known density, thickness and effective atomic number distributions is arranged, that based on the mammograms of the comparison pattern generated at different energies, the atomic number connection parameters with the difference and with the ratio of logarithms of the number of photons that pass through the mammary gland without interacting at two different radiation energies, and that, based on the parameters of this compound, the distribution of the atomic number in the mammary gland is determined by the equation